How to slove last 2 question.
2. National Scan, Inc., sells radio frequency inventory tags. Monthly sales for a seven-month period were as follows: Month Sales (000 units)
Feb. 19
Mar. 18
Apr. 15
May 20
Jun. 18
Jul. 22
Aug. 20
a. Plot the monthly data on a sheet of graph paper.
|
Month
|
Sales
(000)Units
|
|
Feb.
|
19
|
|
Mar.
|
18
|
|
Apr.
|
15
|
|
May
|
20
|
|
Jun.
|
18
|
|
Jul.
|
22
|
|
Aug.
|
20
|
|
b. Forecast September sales volume using each of the following:
(1) A linear trend equation.
|
t
|
Y
|
tY
|
|
1
|
19
|
19
|
|
2
|
18
|
36
|
|
3
|
15
|
45
|
|
4
|
20
|
80
|
|
5
|
18
|
90
|
|
6
|
22
|
132
|
|
7
|
20
|
140
|
|
|
|
|
28
|
132
|
542
|
|
|
|
|
|
with n = 7, St = 28, St2 = 140
|
|
b
|
=
|
nSty - StSy
|
=
|
7(542) - 28(132)
|
=
|
.50
|
|
nSt2 - (St)2
|
7(140) - 28(28)
|
|
a
|
=
|
Sy - bSt
|
=
|
132 - .50(28)
|
=
|
16.86
|
|
n
|
7
|
|
For Sept., t = 8, and Yt = 16.86 + .50(8) = 20.86 (000)
|
(2) A five-month moving average.
|
MA5
|
=
|
15 + 20 + 18 + 22 + 20
|
=
|
19
|
|
5
|
(3) Exponential smoothing with a smoothing constant equal to .20, assuming a March forecast of 19(000).
|
Month
|
Forecast
|
=
|
F(old)
|
+
|
.20 [Actual - F(Old)]
|
|
April
|
18.8
|
=
|
19
|
+
|
.20 [18 - 19]
|
|
May
|
18.04
|
=
|
18.8
|
+
|
.20 [15 - 18.8]
|
|
June
|
18.43
|
=
|
18.04
|
+
|
.20 [20 - 18.04]
|
|
July
|
18.34
|
=
|
18.43
|
+
|
.20 [18 - 18.43]
|
|
August
|
19.07
|
=
|
18.34
|
+
|
.20 [22 - 18.34]
|
|
September
|
19.26
|
=
|
19.07
|
+
|
.20 [20 - 19.07]
|
|
(4) The naive approach.
20000
(5) A weighted average using .60 for August, .30 for July, and .10 for June.
0.60(20) + 0.30(22) + 0.10(18) = 20.40
c. Which method seems least appropriate? Why? ( Hint: Refer to your plot from part a. )
d. What does use of the term sales rather than demand presume?